No idea.
I've searched but I can't find a thread that I'm sure I read about this before.
It was a couple of years ago so things might have changed but as I recall you could keep your email forever for about £1 per month.
You won't be able to send mail (from outlook / thunderbird etc) via relay.plus.net after you cancel (Unless you are visiting someone with a plusnet account) but you should be able to send it via your new providers SMTP server.
I can't remember how long you will be able to receive mail and use webmail but I don't think it's turned off as soon as you cancel.
Hopefully someone will pick this up tomorrow.
